Construction for dampening engine noise



Oct. 1, 1957 J. J. MEYERS CONSTRUCTION FOR DAMPENING ENGINE NOISE FiledJuly 20, 1955 I I Ill/ll I/IA l I l I 1/ Ill/I/I/l/f z I I I I A a ll.igl

IN VEN TOR.

m m l. n M J United States Patent O CONSTRUCTION FOR DAMPENING ENGINENOISE John J. Meyers, Rochester, N. Y., assignor to Eastman KodakCompany, Rochester, N. Y., a corporation of New Jersey Application July20, 1955', Serial No. 523,311

3 Claims. 01. 181-33) This invention relates to a construction adaptedto the dampening of disturbing noise such as engine no se byconstructing walls enclosing the source of the noise in the form of amultiplicity of cells in accordance with the sounds which are to bereduced in intensity.

The operation of certain types of machines produces noises which may bedisturbing and disagreeable to many individuals. One type of machinewhich is especially objectionable noisewise is the Jordan engineemployed in paper mill operations. Other types of machinery theoperation of which may produce disturbing noises are generators, sawmills, hammer mills, punch presses, rolling mills, ball mills, and thelike. Machinery of that nature located in the vicinity of residentialareas may interfere with the peaceful enjoyment of property by theresidents thereof and the noise so produced may even be considered anuisance in many instances.

Previously sound absorbing materials consisting ordinarily of some typeof fibrous material have been employed to act as a sound dampenerusually without regard to the frequencies of the sound encountered. Inmany cases sound absorbing material has been employed in the walls ofthe building itself rather than by surrounding the machine responsiblefor the noise with a sound absorbing hood or Walls immediatelysurrounding the noise producing machine.

One object of my invention is to provide a sound absorbing constructiongoverned by the principal frequencies of the noise which is to bedampened. Another object of my invention is to provide a soundproofingconstruction which can, if desired, be employed to immediately surroundthe noise producing machine. A further object of my invention is toprovide a noise reducing construction using acoustical tile of a typewhich is readily available from commercial sources. Other objects of myinvention will appear herein.

In its broadest aspects my invention comprises surrounding the noiseproducing machine or engine with a wall construction designed to accordwith the principal frequencies of the sound which is to be reduced. Inorder to determine the desired structure for the sound reducing walls aspectrum of the noise from the offending machine is first taken. Thesurrounding walls are then designed and constructed to correspond to theoffending frequencies as will be more fully described.

I have found that if the containing walls surrounding the noiseproducing machine or machines are composed of a plurality of cellshaving dead air spaces of volumes related to the noise producingfrequencies the inner construction of which walls are of acoustical tilethe holes of which open only to the dead air spaces of the cells thepresence of these cells in the containing walls dampen or absorb theoffensive sound waves and diminish or eliminate the noise produced bythe noise producing machine. The volume of the air space in the various2,808,122 Patented Oct. 1, 1957 cells to be employed are determined inaccordance with the formula:

21r V V(L+AL) in which formula F is one important frequency of the noisein cycles per second; C is the velocity of sound in air (1100 feet persecond at 70 F.); N is the number of holes in the perforated board ortile which will be open to the dead air space of the cell; A equals thearea of each perforation in square feet; V is the volume of the airspace of the cell in cubic feet: L equals the depth of each hole in feetand AL is l.7 the radius of each hole in feet. The dimensions of thecells are chosen so that no one of their dimensions is in excess of onehalf a wave length of the incident sound which is to be attenuated.

The accompanying drawings illustrate the construction which is employedfor surrounding a noise producing machine, in this case a Jordanmachine. Fig. l is an end elevation view of the Jordan machine 2surrounded by containing walls the construction of the walls not beingshown in detail. Fig. 2 is a view in section of wall construction inaccordance with my invention. The walls surrounding the noise producingmachine are made up of a series of cells the volume of dead air space ofthese cells being determined by the offending frequencies of the noise.The number of each size of cell employed is determined by the percentageof total noise which occurs in each frequency band for which the cellsare being employed, and the various cell sizes are dispersed uniformlyon all surfaces of the sound enclosure. As shown in Fig. 2 one type ofcell employed requires an air space of definite size which is largewhereas other offending frequencies require cells having air spaces ofless volume.

The walls as shown in Fig. 2 consist of an outer layer which in thiscase is A" asbestos board designated 11 applied over /2" plywood boarddesignated 12. The outer layer may, however, be of any suitableconstruction such as plywood sandwiched between stainless steel layersor some other desired construction. Seals are preferably provided wherepipes or other connections pass through the enclosure and between theenclosure and the floor. Such seals may be sponge rubber, etc. However,with this resonant type sound cancellation enclosure it has been foundthat a considerable amount of sound leakage surface can be permittedwithout detrimental effects. The inner walls are made up of fiber glassacoustical tile 13 which conveniently may come in units of 12" x 12" Xor many other sizes. This tile is used with the perforation side facingthe dead air space and the unbroken side toward the noise producingengine. The unbroken side may be covered by a moisture-proof layer suchas of rubber or plastic. The sides of the air spaces instead of fiberglass acoustical tile may be any type of wall or fiber board carryingholes of a satis factory depth. For instance, materials sold under thetrade names: Celotex, Masonite, Insulite, Johns- Mansville and the likemay be used provided that the material is penetrated by holes.

A true resonate cell will peak very sharply at its specific designfrequency having little sound attenuation benefits on either side ofthis frequency. However, if a layer of sound diffusing media isincorporated at the inlet to the throat of the resonator channel thesound waves are diffused and a broadened frequency band attenuationeffect is achieved from the resonator. By using commercial acousticaltile having perforations which extend only part way through the tile,the impunched material remaining at the end of each perforation channelacts as the required diffusion layer within the channel throat. Further,if a tile is used wherein the perforation does penetrate the entire tilethickness, then this same effect can be achieved, by fillingtheresonator volume very loosely with materials such as low. density fiberglass, glass silk, etc. Further this filled resonator can also be usedin conjunction with tiles not punched all the way through to achievestill broader attenuation effects relative to the sound frequency scale.The air spaces of the walls are spaced, by meansof furring-strips 15 ofvarying thickness. to accommodate the cells to the differentfrequencies, which are met with. These furring strips may be anysuitable material suchv as metal or plastic.

The sections illustrated in Fig. 2 are held together by means of battens14 and the sides and-top of. the containing structure are made insections for quick removal which sections maybev secured by-hasps 16.Fig, 3 illustrates the perforated side of acoustical tile or other boardused for the inner walls and Fig. 4 is a sectional view taken on line 44of. Fig. 3-to,illustrate tile construction.

In the case of the operation of a particular Jordan engine it wasdetermined thatv the principal noise produced by that engine inprocessing paper pulp as shown by. a spectrum of that noise was atfrequencies of 260, 525 and 1,050 cycles per second. Thus itappeared'that in accordance with my invention cells of 3 different sizeswould be desirable in enclosing the Jordan engine to reduce the sound.The noise level resulting from the operation of the Jordan engine Wasmarkedly reduced by the construction shown and was particularlyeffective at the peak frequencies.

For the cells to dampen noise of 260 cycle frequency a 2 /2" depth wasdesirable.- Where an acoustical tile was used having dimensions of 12'.x 12" x A" the tile had 196 holes of 32." diameter and /8" depth. Usingthis material in construction leaves 168 acting holes facing theinside'of the cavity. By substituting these values-in the formula giventhe depth of the air spaces for cells to dampen .260 cycle noise was.found to be 2.52".

The size of other cells was? determined by inserting these values inthe. formula. With a 525 value for the frequency, the depth of airspacein this case figured as approximately For the frequency of 1,050 cyclescells having a dead air space of approximately A are indicated using thedimensions given for the cells which were constructed. If acousticalboard 'or tile, of different dimensions or different numbers or depths.of holes or holes of different size areused the cell. spacewould haveto. befigured out using those different dimensions.

By the use of hoods providedwithcells havingzthe calculated. volumes ofdeadair space the noise'andpar: ticularly the peak noises are definitelyreduced toa substantial extent.- Ourinvention maybeemployeddnconstructions in which each individual offending.;unit:is;em closed with walls having cells-.of the described construction or theentireroomwhere oneorseveral of these machines are found may beenclosedincorporatin'g:the machines in. one roomhaving a wall.construction consisting of cells of the type describedtoabsorb the peaknoises which issue therefrom.

I'claim:

l. A cell adapted for use. in soundinhibiting con struction whichcomprises a sealedjenclosure having on one side a sheet ofacousticalmaterialprovided with perforations. opening only to the dead airspace offll cell and on the outer layer a sheetof solid materialthe air spaceofsaid cell conformingin volume :to that which results fromdeterminingthe same in the following formula inhibited;

in which formula F=a sound frequency in cycles per second; C=thevelocity of sound in air; N =the number of holes in the perforatedmaterial opening to the dead air space of the cell; A=the area of eachperforation in square feet; V=the volume of air space of the cell incubic feet; L= he depth of each hole in feet; AL=1.7 the radius of eachhole in feet.

2. A noise minimizing. construction to surround a noise-producingmachine, the spectrum of the noise of which. shows a plurality ofprincipal noise, producing frequencies, which comprises Walls made up ofa series of cells the length and width of which are accommodated to thedimensions of acoustical sheet material employed to form a portion ofthe wall construction which acoustical material is providedwithperforations opening only into the cell, the inner and outer layersof the cells being so spaced as to provide volumes of air spaces in thecellscorrespondingtorespective principal frequencies of the noisewhichvolumes are determined in accordance with ,theformula in which formulaF=a principal frequency of the sound in cycles per second; C=thevelocity of sound in air (1100, ft; per. sec. at F.); N=the number ofholes inthe perforatedmaterial which open to the dead air space ofthecell; A=the area of each perforation in square feet; V=the volume of.air space of the cell in cubic feet;'L=th'e depth of .each hole .infeet; AL=1.7 the radius of' each hole in feet; the various cells beingemployed" in approximately the percentage of the total noise identifiedwith each principal frequency, the various cell sizes. being disperseduniformly. throughout the sounden'closure.

3. A sound inhibiting construction to inhibit the noise produced by aJordan engine, the spectrum of the noise of which' shows the principalnoise frequencies to be 260, 525, and 1050 cycles per secondwhichcomprises enclosing the engine with walls, of sealedcells enclosing deadairspace, of three diiferentsizes, the inner walls of' the cells beingof acoustical sheet material having perforations therein openingonlyonto the dead air space of-the cell and the outer walls of the cellsbeing of solid sheet material, the air spaces of the cells employed insuch construction.corresponding to that determined in accordance withthe formula:

in which formula-F=a principal frequency of the sound in cycles persecond; C=the velocity of sound in air (1100 ft. per sec. at 70 F.);N=the number of holes in the perforated material which open to the-deadair space of the cell; A=the area of each perforation in square feet;V=thevolume of air space of the cell in cubic feet; L=the depth of' eachhole in feet; AL=1.7 the radius of each hole in feet.

References Cited in the file of this patent- UNITED STATES PATENTSGrutzner July 12, 1938 Eckardt' Jan. 27, 1942 OTHER ,REFERENCESAbsorptionCharacteristics of Acoustic Material With PerforatedFacings.Ingard et al. The Journal of the Acoustical Society of: America.September 1951, pp. 533-540:

The use of.Perforated Facings in Designing Frequency Resonant Absorbers.Calloway et al. The Journal of the Acoustical Society of America. May1952, pp. 309-312.

